The UCLA Integrated Substance Abuse Programs (ISAP), in collaborations with the Washington State Department of Corrections (WSDOC) and CiviGenics, Inc., is proposing a 5-year study to assess (1) the differential clinical effectiveness and cost-effectiveness of long-term residential treatment versus intensive outpatient treatment in a prison-based treatment setting and (2) to determine whether either treatment modality is more effective for drug-involved offenders matched to either treatment modality (e.g., based on risk level and/or substance abuse severity). Research has demonstrated the effectiveness of both therapeutic community and less intensive cognitive-behavioral treatment approaches to treating drug involved offenders in prison settings. However, these two treatment approaches differ in terms of duration and intensity of treatment services, and no empirical research has examined the differential effectiveness and cost-effectiveness of these two treatment approaches as they pertain to drug-involved offenders in prison. Eight hundred inmates (600 males and 200 females) will be randomly assigned to 9-month long-term residential (LTR) or 12-week intensive outpatient (IOP) prison-based treatment. Study participants will be assessed in face-to-face interviews at the time of recruitment (baseline), immediately prior to discharge from the treatment programs and release from prison (pre-release), and at 12-months following their release from prison and completion of in-prison treatment. In addition, WSDOC will provide records-based data on post-release treatment participation, illicit drug use (i.e., results of drug tests), and return-to-custody rates during the follow-up period. The study has the following primary aims: (1) Examine the differential effectiveness of LTR versus IOP treatment in a prison-based treatment setting. (2) Determine whether prison-based LTR or IOP treatment is more effective for drug-involved offenders who are appropriately matched to LTR or IOP treatment (e.g., based on risk level, substance abuse severity). (3) Examine the cost-effectiveness of LTR versus IOP treatment in a prison-based treatment setting. Correction departments are increasingly providing prison-based treatment to drug-using offenders. The results of this study will have potentially significant financial and policy implication to state legislatures, policy-makers, and corrections departments in terms of how increasingly limited financial resources are allocated to the treatment of drug-involved offenders.